On Benjamin's 18th day in Israel he stands in the shade of a palm tree in the paved courtyard of an absorption centre that will be his home for the next six months. On his head he wears a kippah and around his neck a chain carrying his name in Hebrew lettering.

He is one of the latest young Jewish Iranians to leave their homeland in search of a new life in Israel at a time of growing tensions between the two nations.

Once Benjamin, 23, was teaching Hebrew and running a shop in Iran. Two years ago he was arrested by Iranian intelligence agents who threatened to kill him and his family.

"They put a gun in my head and forced me to sign that I was a spy for Israel and they said: 'We will kill you'. I thought: 'I'm going to die just for being Jewish,'" he said.

He will not give his real name or have his face photographed for fear of reprisals against his elderly parents who are still in Iran, but he has taken Benjamin as his new name in Israel.

Eventually Benjamin escaped, using an old passport that was no longer registered on Iranian government computers and made his way to Israel with the support of the Jewish Agency, which is responsible for arranging immigration for Jews from across the world in what is known in Hebrew as Aliyah, or the ascent.

Around 20,000 Jews make Aliyah to Israel every year, most arriving under the Law of Return under which the state grants citizenship to anyone with at least one Jewish grandparent.

Not all the new Iranian arrivals have had such harsh experiences. Others in the same absorption centre in east Jerusalem, where they live and take Hebrew classes for six months, say they simply felt suffocated by the current Iranian regime and unable to live freely.

There remains a large Jewish community in Iran of around 25,000 people. Synagogues still function and the Jewish community has a representative in parliament. Yet large numbers from the community have left and settled across the world, particularly in Los Angeles, and this year around 150 are expected to head to Israel.

"This is my country, I feel at home," Benjamin says. He intends to join the Israeli military and serve as a career soldier.

The Jewish Agency, which is funded by donations, has for years helped bring Jewish Iranians to Israel. But only recently, at a time when fevered speculation about the possibility of war with Iran dominates the Israeli media, has it begun to talk openly about its work.

Many elements remain secret, particularly the routes travelled between Iran and Israel.

"In the past year there has been a major increase in immigration from Iran," says Yossi Shraga, the Jewish Agency's expert on Iran who helps bring the immigrants - known as Olim - to Israel.

He says others stay behind partly because the size of the Jewish community in Iran provides a sense of security but also because of the cost of leaving.

Most of those who leave cannot take the money they have earned during their life and if they leave their homes empty the state will eventually confiscate them.

"It's very difficult for them to leave this behind," he says. "That's one of the reasons there's no mass exodus."

The Jewish Agency provides a basket of goods for the new arrivals including free Hebrew lessons, tax exemptions, free healthcare and rent subsidies for the first six months.

Now this year a wealthy Jewish-Christian evangelical organisation has stepped in to encourage more Jewish Iranians to make Aliyah to Israel by offering an additional $10,000 per person.

The International Fellowship of Christians and Jews is run by an American-born rabbi, Yechiel Eckstein, who has spent years working with the Christian Evangelical community in the US, encouraging them to donate to Jewish causes, particularly Aliyah.

Rabbi Eckstein says the group takes no political stance and he notes that some of their money supports the Arab Bedouin community in Israel, although funds also go to the municipality at Ariel, one of the largest Jewish settlements in the Israeli-occupied West Bank.

Some in the Jewish community have criticised his relations with evangelical Christians, among them a number of high-profile rabbis who issued a ruling against accepting money from his fellowship.

However, Rabbi Eckstein says his Christian supporters share his goals.

"They believe, and I believe, that they have a very important role in helping facilitate the in-gathering of the Jewish people as foretold and promised by Isaiah and the prophets and this is part of the messianic redemptive process," he says.

His group's money has supported Jews from across the world to make Aliyah, but is now focused on Iran where he suggests the Jewish community is threatened as it was in Hitler's pre-war Germany.

But he also says Aliyah has a clear political dimension within Israel, particularly to ensure a Jewish majority persists in a country that has a 20% Arab minority, not counting the 4 million Palestinians who live in the occupied territories.

Relations between Israel and Iran have not always been so bad. Before the Islamic revolution in 1979 there was close co-operation between the two governments.

Even now, amid the hostility surprising links remain, not least a daily radio programme produced in Jerusalem for the past 48 years and broadcast into Iran in Farsi.

Every Sunday evening, after reading the news, Menashe Amir takes calls from Iranians on his 90-minute show.

On one recent broadcast Amir, 67, who himself emigrated from Tehran in 1959, had dozens of listeners, all apparently Muslim Iranians, calling in to condemn the capture of the US embassy in Tehran in 1979 and the 444-day hostage crisis that followed. Often they are also highly critical of the Palestinians and other Arab nations.

None give their names and they dial a number in Germany which is re-routed to Amir's studio at the Israel Broadcasting Authority in Jerusalem, in a stone house built in 1903 for the wife of the King of Ethiopia.

His programme has advertised the $10,000 incentive offered by Rabbi Eckstein's group and the recent immigrants say they were eager listeners to his show from their homes in Tehran. On the programme he is openly critical of the Iranian regime.

"I think that the Iranian regime comprises a threat to the whole of humanity not only Israel. They are a danger for the whole universe because of their ideology," he says after the broadcast.

He says he feels the Jewish community in Iran is threatened, particularly if there is a war.

"It's not important for me where the Jews go when they leave Iran," he says, "but I advise them not to stay because they don't have any cultural or secure future in Iran."